package com.mida.bms.report.util;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;


/**
 * Base64编码工具类
 * @author conyfrommars
 *
 */
public class Base64 {
	
	 private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_".toCharArray();

     public static String encode(byte[] data) {
         int start = 0;
         int len = data.length;
         StringBuffer buf = new StringBuffer(data.length * 3 / 2);

         int end = len - 3;
         int i = start;
         int n = 0;

         while (i <= end) {
             int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 0x0ff) << 8) | (((int) data[i + 2]) & 0x0ff);
             buf.append(legalChars[(d >> 18) & 63]);
             buf.append(legalChars[(d >> 12) & 63]);
             buf.append(legalChars[(d >> 6) & 63]);
             buf.append(legalChars[d & 63]);
             i += 3;
             if (n++ >= 14) {
                 n = 0;
                 buf.append(" ");
             }
         }
         if (i == start + len - 2) {
             int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 255) << 8);
             buf.append(legalChars[(d >> 18) & 63]);
             buf.append(legalChars[(d >> 12) & 63]);
             buf.append(legalChars[(d >> 6) & 63]);
             buf.append("=");
         } else if (i == start + len - 1) {
             int d = (((int) data[i]) & 0x0ff) << 16;
             buf.append(legalChars[(d >> 18) & 63]);
             buf.append(legalChars[(d >> 12) & 63]);
             buf.append("==");
         }
         return buf.toString();
     }
     private static int decode(char c) {
         if (c >= 'A' && c <= 'Z')
             return ((int) c) - 65;
         else if (c >= 'a' && c <= 'z')
             return ((int) c) - 97 + 26;
         else if (c >= '0' && c <= '9')
             return ((int) c) - 48 + 26 + 26;
         else
             switch (c) {
                 case '-':
                     return 62;
                 case '_':
                     return 63;
                 case '=':
                     return 0;
                 default:
                     throw new RuntimeException("unexpected code: " + c);
             }
     }

     /**
      * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned.
      */
     public static byte[] decode(String s) {
         ByteArrayOutputStream bos = new ByteArrayOutputStream();
         try {
             decode(s, bos);
         } catch (IOException e) {
             throw new RuntimeException();
         }
         byte[] decodedBytes = bos.toByteArray();
         try {
             bos.close();
             bos = null;
         } catch (IOException ex) {
             System.err.println("Error while decoding BASE64: " + ex.toString());
         }
         return decodedBytes;
     }

     private static void decode(String s, OutputStream os) throws IOException {
         int i = 0;
         int len = s.length();
         while (true) {
             while (i < len && s.charAt(i) <= ' ')
                 i++;
             if (i == len)
                 break;
             int tri = (decode(s.charAt(i)) << 18) + (decode(s.charAt(i + 1)) << 12) + (decode(s.charAt(i + 2)) << 6) + (decode(s.charAt(i + 3)));
             os.write((tri >> 16) & 255);
             if (s.charAt(i + 2) == '=')
                 break;
             os.write((tri >> 8) & 255);
             if (s.charAt(i + 3) == '=')
                 break;
             os.write(tri & 255);
             i += 4;
         }
     }
}
